Transmissibility of mpox to the general population from travellers returning to South Korea

Based on data from three imported mpox cases in South Korea, the overall attack rate was determined to be 1%, while a secondary attack rate of 14% was estimated in the high-exposure group.

In East Asia, mpox was initially detected in June 2022 (South Korea) among returning travellers who had engaged in sexual activity with men from Europe.As of May 2023, several European countries had reported a single-digit incidence of mpox infections, seemingly indicating the end of the epidemic. 1By contrast, East Asia, including China, Japan, South Korea and Taiwan, has continued to report an increase in the incidence of mpox infections. 1 A recent study demonstrated the importance of prioritizing public health and social measures, including mpox vaccination of high-risk subpopulation, to reduce mpox transmission across the community. 2However, epidemiological data on Asian countries remain lacking. 3,4Therefore, this study examined the transmissibility (i.e.attack rate) of mpox using contact-tracing data from the first three imported cases in South Korea.
We collected publicly available data on mpox cases from Korean public health authorities (Supplementary Material).Based on the contact-tracing data of the imported mpox cases, the degree of exposure among individuals who had come into contact with the confirmed cases was categorized as follows: 'high degree', 'intermediate degree' and 'low degree' (Supplementary Material). 5e measured the overall attack rate, which is the probability that an infection occurs among susceptible individuals, and the secondary attack rate in the high-exposure group and estimated the 95% confidence intervals (CIs) using the bootstrap method (Supplementary Material).
The overall attack rate based on the first three imported cases was found to be 0.9% (1 out of 106; 95% CI, 0.0-2.8%).After stratification by degree of exposure, the secondary attack rate was estimated at 14.2% among contacts in the highexposure group (1 out of 7; 95% CI, 0.0-42.9%).However, no transmission cases were identified in the intermediate-and low-exposure groups (Table 1).
The secondary attack rate provides useful information on how the interactions in a specific setting relate to the transmission risk.Our findings suggest that mpox transmissibility from the first three imported cases to the South Korean population was low and that mpox transmission was potentially driven by the high-exposure group.This finding is consistent with those of previous studies in that the major risk for mpox transmission was associated with a high degree of exposure, including sexual contact. 4Therefore, to prevent delayed diagnoses and reporting, mpox vaccination and awareness campaigns among high-risk populations need to be prioritized. 6otwithstanding, this study has certain limitations.First, behavioural heterogeneity might have influenced the estimation of the attack rate.Thus, further research involving a greater number of cases with contact-tracing data is warranted to avoid possible bias and to reduce CI width.Second, a secondary mpox infection from the imported case occurred during medical practice. 7Therefore, the secondary attack rate in our study might have been overestimated.
The continual estimation of mpox transmissibility is important for evaluating control measures against mpox.A comparison of transmissibility estimates according to different mpoxexposure levels and modes of transmission (e.g.homosexual or bisexual contact) is warranted.Furthermore, with the easing of SARS-CoV-2-related international travel measures in Asian countries, 8 travel advice and active case findings of mpox for the Note: Based on the degree of mpox exposure, individuals were categorized into 'high degree' (unprotected direct contact with a confirmed case or high-risk environmental contact), 'intermediate degree' (unprotected exposure to infectious materials and droplets or potential exposure to aerosols) and 'low degree' (protected from physical or droplet exposure or no physical contact and minimal chance of exposure to droplets) groups. 5

Table 1 .
Descriptive summary of the demographic and epidemiological characteristics of the first three imported mpox cases in South Korea